1. Field of Invention
This invention relates in general to Global Positioning System (“GPS”) receivers, and in particular to a network aided GPS systems.
2. Related Art
Cellular telephony, including the use of Personal Communication System (“PCS”) devices, has become commonplace. The use of such devices to provide voice, data, and other services, such as Internet access, has provided many conveniences to cellular system users.
A current thrust in the cellular and PCS area is the integration of Global Positioning System (“GPS”) technology into cellular telephone devices and other wireless devices. For example, U.S. Pat. No. 5,874,914, issued to Krasner, which is incorporated by reference herein in it's entirety, describes a method where a basestation (also known as the Mobile Telephone Switching Office (“MTSO”)) transmits GPS satellite information, including Doppler information, to a remote unit using a cellular data link, and computing pseudoranges to the in-view satellites of the GPS constellation without receiving or using satellite ephemeris information.
This current interest in integrating GPS with cellular telephony stems from a Federal Communications Commission (“FCC”) requirement that cellular telephones be locatable within 50 feet once an emergency call, such as a “911” call (also referred to as Enhanced 911 or “E911”) is placed by a given cellular telephone. This position data assists police, paramedics, and other law enforcement and public service personnel, as well as other agencies that may need or have legal rights to determine the cellular telephone's position. Further, GPS data can be used by the cellular user for directions, location of other locations that the cellular user is trying to locate, determination of relative location of the cellular user to other landmarks, directions for the cellular user via Internet maps or other GPS mapping techniques, etc. Such data can be of use for other than E911 calls, and would be very useful for cellular and PCS subscribers.
However, since cellular telephones can travel into areas where GPS signals cannot be reliably received, augmentations to the GPS system are being researched to support the E911 and other GPS/cellular applications. GPS is increasingly being pressed into service in the cellular telephone/PDA/mobile computer application where a solution is required in areas with substantial blockage, such as inside buildings, in subway stations, and other areas where the system RF link budget is unable to sustain communications with mobile units that travel into hostile signal reception environments such a buildings. Pseudolites are well-known commercially available ground-based transmitters which augment the orbiting GPS constellation with one or more additional transmitters to improve the availability and quality of a GPS solution. Current pseudolite applications include local-area augmentation system (“LAAS”) transmitters for precision approach.
At present a number of different types of GPS assistance or aiding systems and architectures are known. Examples of these systems include aiding system designed and produced by companies such as Qualcomm of San Diego, Calif. and SiRF Technology, Inc. of San Jose, Calif. Generally, any type of aiding and/or assisting in obtaining a GPS location is referred to as Aided GPS (“AGPS” or “A-GPS”).
Unfortunately, the different type of aiding systems presently known only support known AGPS functionalities and lack the capability of providing “anytime and anywhere” positioning and better location application support.